In ignition control systems known in the prior art, the ignition timing is advanced in the idling domain of the engine by an amount which increases when the engine speed drops. The shift takes place between two engine speed values both of which lie substantially in the idling range of the engine. The control signal for this shift is provided by a rotating transducer assembly. In one such apparatus, described in the German Patent Disclosure Document DE-OS 2 807 499, to which U.S. application Ser. No. 12 802, filed Feb. 16, 1979 corresponds, now abandoned, the spark advance is used to stabilize the engine operation in the idling domain, in particular if the engine is suddenly subjected to additional loads, for example by an electrical load switched on due to the use of, for example, air conditioning, etc. When the engine speed drops due to the additional load, the spark advance counteracts this tendency and results in overall stabilized operation. Inasmuch as the degree of spark advance is limited, the advance must be defeated and the engine timing returned to normal when the engine speed drops below a given lower rpm. This lower speed is preferably chosen to lie below the lowest normally occuring engine speed. It is a disadvantage of this apparatus as well as the other known systems of the prior art that they are cumbersome and expensive and thus not really suitable for use as input circuits in ignition timing systems. This is particularly the case when these inputs circuits are to be integrated with the transducer assembly.